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-   -   transition in SA turbulence model (http://www.cfd-online.com/Forums/fluent/34779-transition-sa-turbulence-model.html)

wassim October 6, 2004 14:06

transition in SA turbulence model
 
hi, i was wondering if somebody have tried to work on transition from laminar into turbulent for the Spalart-Allmaras model. comparing the equations used in Fluent to the ones given by the original model it seems it is missing the source term related to transition point and i was trying to add that to the model but i'm facing some problems..

SAM October 9, 2004 07:20

missing terms in SAturbulence model
 
r u sure

wassim October 12, 2004 14:51

Re: missing terms in SAturbulence model
 
yes, if u compare the paper published by S-A and the equations used in Fluent you will see that the terms concerning the Laminar sublayer are ommitted however this might be replaced by Fluent with the way they calculate their stress equations at the first cell i'm still checking that however there is the last term concerning the fixed transition that S-A uses in their model (ft2*deltaU^2) this is replaced in Fluent by a source term that can be added by the user through a UDF.

SAM October 13, 2004 01:05

Re: missing terms in SAturbulence model
 
fluent has already mentionaed that it is low reynolds number model but they aslo said in next paragraph that this can be applied to fully turbulent flow like k-epsilon model

see fluent users guide turbulence modeling

wassim October 14, 2004 14:01

Re: missing terms in SAturbulence model
 
for a fully turbulent case, i have no problem but what about cases where there is transition, i mean S_A in Fluent doesnt predict transition it is a fully turbulent model. i tried to do that by seperating the mesh into laminar and turbulent region and this was reflected with better results in my CL and CD but this solution is not practical so what i'm trying to do now is to add some adjustment as a UDF in order to model transition and thus improve my calcualtions.. i really approciate your comments on the subject, thanks


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